Surface for water vehicles



Feb. 25, 1969 P. c. JOHNSON SURFACE FOR WATER VEHICLES Filed Dec. 27. 1966 m M my 6 A w United States Patent 6 Claims ABSTRACT OF THE DISCLOSURE An improved water contacting surface for use in connection with articles designed for movement over water, the surface being provided with a pattern of parallelly disposed grooves for providing optimum lift/drag ratios. The formula defining the configuration is substantially Y=a sin bx wherein Y is the distance across the water contacting surface, and wherein a and b are optimized constants. Preferably, the preferred equation is as follows:

Y:=.08 sin (10.05x)

This invention relates generally to articles designed for movement over water and more particularly to the water contacting surfaces of such articles such that maximum stability and minimum drag results as the article moves over the water surface.

It has long been a problem in the field or marine engineering to produce surface moving articles and vehicles having a high degree of stability, maximum maneuverability with a minimum of chattering under all types of surface conditions and a minimum drag factor. One specific answer to these problems has been the evolution of catamaran type hulls which create, in accordance with their design, a degree of lift to minimize the drag factor while providing, again with their design, a high stability factor.

In accordance with these desirable qualities, applicant has provided a new and unique Water contacting surface which includes a plurality of longitudinally arranged and and properly designed grooves for use with articles and vehicles designed for movement over water which does provide a high lift factor to reduce the drag factor and which increases the maneuverability, control and stability of the article.

It is therefore an object of applicants invention to provide a surface for articles designed to move over water while assuring maximum stability and maneuverability under all water surface conditions.

It is a further object of applicants invention to provide a surface for articles moving over water which includes a plurality of longitudinally extending grooves to provide a maximum lift factor for the articles due to an optimum air entrapment situation developed by the groove configuration.

These and other objects and advantages of the invention will more fully appear from the following description, made in connection with the accompanying drawing, wherein like reference characters refer to the same or similar parts throughout the several views and in which:

FIGURE 1 is an illustrative view showing one of the articles upon which the concepts of applicants invention may be utilized;

FIGURE 2 is a bottom plan view of a water ski embodying the concepts of the invention;

FIGURE 3 is a longitudinal section taken substantially along line 33 of FIGURE 2;

FIGURE 4 is a transverse section taken substantially along line 4-4 of FIGURE 2; and

3,428,979 Patented Feb. 25, 1969 FIGURE 5 is a section similar to FIGURE 4 showing a modified form of groove configuration.

In accordance with the accompanying drawings, applicants concept is illustrated on the water contacting surface or bottom of a water ski.

The ski generally designated 10 is of generally rectangular configuration having a broad transverse dimension to provide a water contacting bottom surface 11 and a load supporting top surface 12 spaced apart by a relatively smaller vertical dimension. Ski 10 is provided with, as normally known, an upwardly curved and transversely radiused tip 13, and again, as is common in many water skis, a gradually transversely tapered rear or tail section 14. To this point the ski is no different than those skis readily available on the commercial market.

To incorporate applicants concept to ski 10, a plurality of grooves 15 are provided in transversely spaced, longitudinally extending relation on the bottom surface 11 of the ski 10. The forwardmost end 15a of grooves 15 is approximately vertically below the initial point 13a of upward curvature of the ski tip 13. This forward groove end 15a is produced by extending the grooves 15 along the ski bottom 11 while the ski is curved upwardly which provides a groove of increasing depth, as illustrated in FIG- URE 3, to an upper depth limit as the groove 15 is followed from front 15a to the rear of the ski.

The depth and shape of the respective grooves generally designated 15 has been determined experimentally and as a result, the shape of the grooves 15 is ideally a sine wave configuration, and more specifically consists of a curve having the basic formula: y:a sin bx.

Initial testing before this formulation was confirmed included testing of V-shaped grooves varying from .05" to .25" inch in depth and up to 1.3 inches in width. The thickness of the ski was 4 inch in all instances.

Continued testing included the consideration of simple shallow V-shaped grooves to grooves having a sine wave configuration matching the formula Y=a sin (bx and c) with each shape being tested under virtually the same conditions. In terms of the thickness of the article, various amplitudes were tested ranging from 6 percent to 33 percent of thickness, with a result that an amplitude of 21 percent was found to provide the desired qualities while still affording suificient strength for the ski. Amplitudes between about 15 percent and 50 percent of the distance between the water contacting surface and the load supporting surface are considered useful. After establishing the value of a to be .08, tests with frequencies ranging from 0 inch to 1.300 inches for a ski of 6 /2 inches in width were performed. These frequencies b expressed in terms of total projected width versus ski width are from 30 percent to 100 percent.

Drag values were recorded by utilizing an in-line spring scale while towing skiers at constant speeds in the boats wake at a distance of feet, and from these drag values it was found that a frequency of .625 produced the minimum drag while affording a high degree of control, stability and maneuverability.

The groove formula then, for a water ski having a thickness of /1 inch and a width of 6 /2 inches is:

Y=.08 sin (10.05x)

These conclusions were of course based on a load factor in accordance with the support area and load thereon, but it should be obvious that the same sine wave groove configuration may be altered with different load factor conditions while still providing a buoyant, water surface moving article having desired qualities of drag, control, and stability.

The grooves 15 in the skis tend to trap air at the forwardmost end 15a thereof to create a lift factor as the ski moves forwardly, actually partially supported [by the air bubbles thereunder. This lift factor results in the ski riding higher in the water to the extent that approximately 50 percent of the grooved ski glides above the water as compared to 30-40 percent of a flat ski gliding above the water.

It is felt that this high ride effect, and hence less drag with a plurality of tracking members as represented by the lowest portion 16 of the grooves 15 remaining in the water, promotes the attributes of stability and tracking while also reducing the physical strength required to control and ride the skis. The plurality of water contacting portions .16 and the sides of the grooves .15 remaining in the water also substantially reduces the tendency to sideslip while sweeping arcs behind the tow boat.

The plurality of grooves 15 having substantially a sine wave configuration extending longitudinally of the ski 10 further increases the longitudinal stability of the ski to prevent tip fluttering as well as producing a plurality of water surface breaking elements as compared to a flat board ski to eliminate the slapping effect usually encountered in high speed or choppy water skiing.

A modified form of the invention is illustrated in FIGURE wherein the bottom of the ski consists of a combination of grooves utilizing mixtures of sine wave curves. This configuration is obtained by varying the as and bs of the basic equation y=a sin bx. In the form shown the uppermost portions 17 of the grooves are in substantially planar relation and two repeating grooves are utilized such that the water contacting portions 18-48 agree to one formulated value while the portions 1919 therebetween agree to another formulated 'value. This configuration is a logical extension of the basic concept of this application and may in certain instances provide benefits over and above those obtainable with the first form. As an example of such a benefit it should be obvious that as speed increases the lift factor may definitely increase due to the enlarged air entrapping area between adjacent larger sine sections 19-19 as compared to that area available in the first form of FIGURE 4.

It should be obvious that the concept of a plurality of longitudinal grooves on the undersurface of an over water moving article is applicable to many similar devices where similar considerations such as stability, control and drag factor are important.

What is claimed is:

1. A water contacting surface for a water ski having a load supporting surface spaced upwardly therefrom including:

(a) a plurality of longitudinally extending grooves arranged to extend over at least a substantial portion of the length of the ski; and

('b) said grooves having a cross sectional shape defined by the formula y=a sin bx where a is the amplitude of the wave, b equals 21:- divided by the Wave length, and where x is the dimension taken transversely along the plane of the water contacting surface and y is the dimension taken normally thereto in the plane extending between the water contacting surface and the load supporting surface, the value of the constant b being about 10.

2. The structure as set forth in claim 1 wherein the amplitude of said groove represented by the constant a is selected from a range of from about 15 percent to about percent of the distance between the water contacting and load supporting surfaces.

3. The structure as set forth in claim 1 wherein the amplitude of said groove represented by the constant a is determined to be about 21 percent of the distance along the plane between the water contacting and load supporting surfaces.

4. The structure as set forth in claim 1 wherein the total groove area transversely of the ski is selected from a range of between about 30 percent to about percent.

5. The structure as set forth in claim 1 wherein said grooves comprise alternating groove sets wherein at least one of said sets is provided with a predetermined factor for the quantity a while at least one of the other of said sets is provided with a different predetermined factor for the quantity a.

6. The structure as set forth in claim 1 wherein said grooves comprise alternating groove sets wherein at least one of said sets is provided with a predetermined factor for the quantity b while at least one of the other of said sets is provided with a different predetermined factor for the quantity b.

References Cited UNITED STATES PATENTS 3,289,227 12/1966 Kelly 9310 FOREIGN PATENTS 373,494 3/ 1907 France. 1,285,809 1/1962 France. 1,108,599 6/1961 Germany.

54,629 11/ 1934 Norway. 395,774 7/ 1965 Switzerland.

MILTON BUCHLER, Primary Examiner.

P. E. SAUBERER, Assistant Examiner.

US. Cl. X.R. 280l 1.13 

